Valve actuating mechanism

ABSTRACT

The invention contemplates a valve-actuating system wherein purely longitudinal displacement is achieved upon relative rotation of members in coaxial, helically cammed relation. A number of different embodiments are disclosed whereby the desired rotation is effected, and illustrative employments are described for valve actuation derived from various cam structures, including a cam with spring-loaded follower, and a desmodromic cam, as well as block-mounted and overhead camshaft forms thereof.

United States Patent Inventor Robert L. Weber 49 Clapboard Hill Road,New Canaan, Conn. 06840 Appl. No. 803,164

Filed Feb. 28, 1969 Patented June 22, 1971 VALVE ACTUATING MECHANISM 51Claims, 17 Drawing Figs.

US Cl 123/90.12, 74/110, 251/229, 251/250, 123/90. 14, l23/90.24,123/90.27, 123/90.28, 123/90.6, l23/90.61

Int. Cl F011 1/04, F011 l/30, F0111/32 Field of Search 123/90, 90.14,90.24, 90.27, 90.28, 90.6, 90.61; 74/1 10; 251/229, 249, 250

Reierenees Cited UNITED STATES PATENTS 4/1917 Kessler 123/90 1,359,669 1H1920 Buck 123/90 1,362,500 12/1920 Moeller... 123/90 1,462,160 7/1923Anthony. 123/90 1,528,193 3/1925 Buck 123/90 1,850,544 3/1932 Gray123/90 2,071,719 2/1937 Wurtele... 123/90 2,609,803 9/1952 Doughty123/90 2,609,804 9/1952 Doughty 123/90 Primary Examiner-Al LawrenceSmith Altarney-Sandoe, Hopgood and Calimafde ABSTRACT: The inventioncontemplates a valve-actuating system wherein purely longitudinaldisplacement is achieved upon relative rotation of members in coaxial,helically cammed relation. A number of different embodiments aredisclosed whereby the desired rotation is effected, and illustra- Liveemployments are described for valve actuation derived from various camstructures, including a cam with springloaded follower, and adesmodromic cam, as well as blockmounted and overhead camshaft formsthereof.

PATENTEUJUNZEIHYI 3,585 974 sum 1 OF 4 TORNE PATENTEUJUNZZIHYI134585.974

SHEET 3 OF 4 it; i Amway IN ENTOR @amrz h/am' VALVE ACTUATING MECHANISMThis invention relates to an improved motion-translating mechanismhaving particular utility when embodied in valveactuating mechanism ofinternal-combustion engines.

The poppet valve used in most of todays internal-combustion engines hassurvived many attempts to improve upon its simplicity and dependability.There have been numerous innovations in valve mechanisms and in methodsof actuating the valve, but because of high cost, inadequatereliability, excessive complexity, or a combination of these factors,few improvements have reached the stage of mass-production, and none ofthese few has long survived the test of the marketplace.

Despite the apparent triumph of the poppet valve, the valve area stillplagues today's high-compression engines, as a major trouble source; incontrast, design considerations for other engine parts, such as pistons,rods, crankshaft, camshaft, cam followers, heads and block have becomefairly well understood and stabilized. Advances in metallurgy have madeit possible to achieve a high degree of operating reliability, providedreasonable care is given to proper lubrication.

Much of the serious trouble begins in the so-called valve train, i.e.the system of push rods, rocker arms, valve guides, springs, valves,etc. Chiefly, the trouble lies in mechanical wear of the valve stem inits guide, due to an actuating force component which is other thanpurely axial. Such nonaxial component is attributable to severalfactors, including angularity" in force transmission from the rocker armto the valve stem, and deliberate off-axis contact between the valvestem and its actuator (to impart indexed valve rotation for betterseating). In operation, the valve-seat bore will depart fromconcentricity with the valveguide bore, and the valve stem mayeventually depart from concentricity with the seat face on the valvemember.

After to 10,000 miles, the average production engine has begun to wearsignificantly in its valve trains, for one of more of the above-notedreasons, because current design cannot help but put some side thrust onthe valve stem, for every actuating stroke. Such wear impairs theability of the valve to seat squarely, and heat-dissipation is adverselyaffected, with rapid deterioration in performance and accelerated wearof the valve, the valve guide and other engine parts such as pistons,rings and cylinders.

It is, accordingly, an object of the invention to provide an improvedvalve-train movement which will eliminate or very substantially reduceengine problems of the character indicated.

It is a specific object to provide a valve-train mechanism which isinherently free of side thrust on the valve stem, for a longitudinallyreciprocating valve system; stated in other words, it is an object toprovide such mechanism in which purely axially oriented reciprocatingforces are generated for valve actuation.

Another object is to achieve the foregoing objects with a constructionin which a net indexing rotational increment is imparted to the valvefor each actuation thereof, thus reducing any tendency to form alocalized hot spot" in the area of valve-seat engagement.

Still another object is to provide an improved valve-actuating mechanismwhich inherently assures full and uniform valve seating for veryextended periods of engine operation, as compared with systems in usetoday.

A further object is to provide an improved valve-actuating mechanismwhich inherently absorbs, by direct reaction to the engine block orcylinder head, a major fraction of valve-accelerating and deceleratingforces, thus reducing wear in cam and follower parts of the valve train.

It is in general an object to achieve the foregoing objects with abasically simple structure, which lends itself to economicmass-production, adjustment, servicing and replacement (if evernecessary), which may use standard valves, which inherently requiresrelatively low actuating forces, which is equally adaptable toconventional cam-andspring-return and to desmodromic or othercam-actuating techniques, and which involves minimum modification ofother parts of the engine.

Other objects and various further features of novelty and invention willbe pointed out or will occur to those skilled in the art from a readingof the following specification in conjunction with the accompanyingdrawings. In said drawings, which show, for illustrative purposes only,preferred forms of the invention:

FIG. 1 is a simplified fragmentary sectional view of aninternal-combustion engine incorporating valve-actuating mechanism ofthe invention, utilizing a single block-mounted cam and spring-loadedfollower to derive valve-actuating displacements;

FIG. 2 is a generally similar but more fragmentary view to illustratethe invention in the context of a desmodromic camand-follower system forderiving valve-actuating displacements;

FIG. 3 is an enlarged fragmentary view, partly broken away and insection, for better illustration of one embodiment of valve-actuatingmechanism;

FIG. 4 is a view similar to FIG. 3 to illustrate another embodiment;

FIG. 5 is a longitudinal sectional view, partly broken, to illustratealternate cam-follower mechanism usable with either ofthe mechanisms ofFIGS. 3 and 4;

FIG. 5A is a fragmentary view in elevation, taken from the aspectdesignated SA-SA in FIG. 5;

FIG. 6 is a fragmentary view similar to FIGS. 3 and 4 to illustrate amodification;

FIG. 7 is a simplified diagram schematically illustrating a furtherembodiment;

FIGS. 8 and 8A are respectively simplified front and side elevationsschematically illustrating a still further embodiment;

FIGS. 9 and 10 are simplified views in elevation, partly broken and insection, and schematically illustrating two further embodiments of theinvention;

FIG. II is a view similar to FIG. I to illustrate an overheadcamshaftemployment of the invention;

FIG. 12 is a simplified view in perspective to illustrate a modifieddesmodromic-cam employment of the invention;

FIG. I3 is a simplified fragmentary side view, taken at a sectionthrough the camshaft, to illustrate schematically the camand-followerparts of FIG. 12; and

FIGS. 14 and 15 are similar simplified diagrams respectively depictingpressure-fluid operated embodiments of the invention.

Briefly stated, the invention contemplates a valve-actuating systemwherein purely longitudinal displacement is achieved upon relativerotation of members in coaxial, helically cammed relation. A number ofdifferent embodiments are disclosed whereby the desired rotation iseffected, and illustrative employments are described for valve actuationderived from various cam structures, including a cam with springloadedfollower, and a desmodromic cam, as well as blockmounted and overheadcamshaft forms thereof.

Referring to FIG. 1 of the drawings, the invention is shown inapplication to a four-cycle intemal-combustion engine comprising a block10 having a cylinder bore 11 for guided reception of a piston 12. A pin13 connects piston 12 to a rod 14, the other end of which is carried ata crank 15 of a crankshaft I6, joumaled on a drive axis I7. A head 18closes the outer end of the cylinder 11 and supports a spark plug 19, aswell as gas porting such as the inlet passage 20, and guide means 21 fororientation of a poppet valve 22; valve 22 is shown in open position topermit the downstroke of piston 12 to draw combustible mixture intocylinder 11. A camshaft 23 is joumaled (by means not shown) on an axisfixed in relation to the drive axis I7 and is driven at one-half driveshaft speed by a suitable synchronizing connection, suggested at 24. Inthe form shown, the face of a cam follower 26 tracks the profile of acam'27 on camshaft 23. Follower 26 includes an elongated shank which isguided in a fixed bushing 28 and which is resiliently urged by springloading at 29 to maintain the tracking relationship.

In accordance with the invention, the conventional tappet and rocker-armrelation between cam follower 26 and valve 22 is completely replaced bymechanism whereby cam-follower reciprocation is translated into rotaryreciprocation of two members, coaxial with each other and with the stem30 of valve 22; a helically cammed relation between the two coaxialmembers imparts straight-line actuation of the valve stem, i.e. free ofside or lateral thrust reaction on the valve stem.

in the form of FIG. 1, one of the two relatively rotatable members isbasically a sleeve or nut 31, and the other is the valve-stem guide 2!,the latter being shown insertably fitted in a suitable receiving bore inthe cylinder head 18 and held by a key pin 32 and a radial shoulder 33as a fixed part of the cylinder-head assembly. Plural balls 34 ridecorresponding helical raceways or grooves in axially overlappingadjacent cylindrical surfaces of members 2ll3l, so that rotaryreciprocation of sleeve 31 effects corresponding but purely axialreciprocation of sleeve 3i and of valve stem 3%, carried therewith.Rotary reciprocation is imparted to sleeve 31 by reaction to the thrustof a rack 35, connected by an elongated push rod 36 to follower 26; rackmeshes with helical threads 37 on the otherwise cylindrical periphery ofsleeve 31. The angle a characterizes the effective inclination of thevalve-stem axis with respect to the rack-reciprocation axis as viewed inFIG. ll; this angle and other related factors will be discussed ingreater detail below, in connection with F IG. 3. It will be understoodthat rack 35 and rod 36 may be provided with greater support asnecessary, as for example that indicated at boss 36' for rod 36; andboss 36 may serve the added function of a frame reference for the upperend of spring 29 in the event that the teeth of rack 35 are straight orsubstantially straight, the dashed outlines in FIG. 1 behind the inlet20 may be taken as schematic suggestion of guide means on the valve bodyfor the nonrotatable guided longitudinal reciprocation of rack 35.

The connection of valve 22 to sleeve 31 is preferably such as to permitrelatively free relative rotation of these parts. In the form shown,this is achieved in the context of a light frictional resistance,occasioned by a preloaded spring 38. The reduced tail 39 of valve stem21 passes freely through a central opening in an end wall 4MB of sleeve31!, and spring 3% is compressed between wall 40 and a retaining washeror snap ring 41, carried at the end of tail 33; if desired, washers maybe provided immediately adjacent the respective faces of wall 40, asshown.

In operation, the valve 22 is open when follower 26 is tracking the lowpoint of cam 27. With ensuing camshaft rotation, follower 26 and rack 35are displaced upwardly, to lift sleeve 31 and to develop clockwiserotation thereof (as viewed upwardly along the valve-stem axis); it willbe understood that such rotation is the reacting result of the describedhelically cammed relation between members 211- 31. Valve-seating occursjust prior to tracking the high part of cam 27; spring 38 thusresiliently loads the valve-seated relation. Upon tracking the downslopeof cam 27, sleeve 3H commences its return stroke before unseating valve22; by the time valve 22 is unseated, sleeve has already begun to rotatein the opposite (counterclockwise) direction. The cycle is completedwhen the valve is fully open, as shown.

it will be appreciated that since torsional friction characterizes theotherwise freely rotatable relation between valve 22 and sleeve 3i,there will be a tendency of valve 22 to track the angular oscillation ofsleeve 31, but that in the course of a plurality of valve cycles, thereis a net unidirectional progression of valve rotation, even thoughsleeve 31 rotates just as much in each direction of rotary oscillation.The detailed explanation of such net unidirectional rotation (orindexing) of valve 22 is not yet completely understood, but it isbelieved in part to be attributable to the fact that upstrokedisplacement of valve 22 is shorter than that of sleeve 31, so thatangular acceleration of valve 22 begins more gently on the upstroke ascompared with more sudden acceleration at commencement of the valvedownstroke. Similarly, angular deceleration of the valve is more gentleat the end of the downstroke than it is at the end of the upstroke. Thevery substantially larger valveseating area at 42 determines abruptachievement of zero rotational speed for valve 22 at the end of itsupstroke, but this is to be compared with the relatively small torsionalforces available to accelerate rotation of valve 22 as it begins itsdownstroke. The net result is to develop more counterclockwise thanclockwise rotation in valve 22, in the long run, so that the valve andits seat may be self-burnishing and assure prolonged accurate seating,with well-distributed heat-dissipation over the entire seat 42, and freeof hotspot development.

In the form shown, precise adjustment of the timed seating of valve 22is available through adjustment of the effective length of rod 36,between follower 26 and rack 35. For this purpose, rack 35 is shownthreadedly engaged to one end of rod 36, with a lock nut 35' to hold theposition. The other end of rod 36 is similarly threadedly engaged tofollower 26 and is locked by nut means 43.

The arrangement of FIG. 2 is generally similar to FIG. 1, except thatpositive cam actuation develops both the upstroke and the downstroke ofthe follower 45. Follower 45 is shown with parallel forks 46-46 pilotingon the camshaft 457 which carries a flat cam plate having a cam groove48. A cam-follower roll 49 on follower 45 tracks the radially inner wallof grove 48 to generate upstroke movement, and it tracks the radiallyouter wall of groove 48 to generate downstroke movement. The other endof follower 45 is provided with a rack 50 (suitably guided by means notshown) to drive a valve-actuating sleeve 51 in the manner discussed inFIG. 1, except that since rack 50 is in front of sleeve 51 (asdistinguished from FIG. 1, where rack 35 is behind sleeve 31), thehelical outer rack-drive threads on sleeve 51 are shown with theopposite direction of helical advance; by the same token, the directionof helically cammed engagement between valve-stem guide 52 and sleeve511 is the opposite of'that shown between members 21-31 in FIG. II. Thenet result of recycled cammed actuation of the valve 53 of FIG. 2 is thesame as in FIG. ll, except that positive actuation of both strokes inFIG. 2 assures greater fidelity of valve programming under high-speedconditions, and the net rotation for incremental indexing of the valveabout its axis will, of course, be the opposite of that in FIG. R.

FIG. 3 is an enlarged sectional view to illustrate an adjustable featureembodied in the valve-actuating mechanism within the coaxial structureof the sleeve 55 and valve-stem guide member 56. FiG. 3 also serves toillustrate the relation of angles involved in rack-pinion engagement andin the helically cammed engagement, respectively.

An adjustable feature within sleeve 55 employs an auxiliary sleeve 55'threaded in a counterbore at the open or tail end of the sleeve 55.Auxiliary sleeve 55' is shown with a reduced aperture in an end-closurewall 57, and the reduced tail 58 of the stem 59 for valve 60 extendsthrough this aperture. As washer 6i seats against the shoulder definingthe reduced end 58, and a spring washer 62 retains the assembly withresilient loading which, it will be recalled, is used to assure seating.Preferably, angularly registering cutouts or slots (not shown) inmembers 6li57, are provided to permit breathing or venting air that mustbe displaced during reciprocating of the valve actuator. Adjustment ofthe threaded advance of auxiliary sleeve 55' within the primary sleeve55 will be seen to develop precise control of valve-stem location, sothat valve 6t) may seat with the desired slight resilient loading viaspring 62. Once the adjusted position is determined, a lock nut 65 isset against sleeve 55 to secure the adjustment.

FIG. 3 serves the additional purpose of illustrating presently preferredangular relationships in my valve-actuating mechanism, for the case ofball coupling between members 55 56. The angle a will be recognized asthe angle between the reciprocating rack 66 and the valve-stem axis, andthe rack teeth have tangential engagement with the helical threads onthe outer surface of sleeve 55; the angle a is thus the complement ofthe angle of helical advance for these threads. The angle (1 preferablyexceeds the angle B, which is the angle of advance for the helix whichdetermines cammed action between the inner and outer members, namely thegrooved part 67 of the valve-stem guide 56 and the bore of sleeve 55.Preferably, the latter engagement utilizes plural equally angularlyspaced like helical grooves or raceways 68, and plural balls arereceived in each of these raceways. The plural balls will be understoodto support the relatively rotatable members throughout the course of theactuating stroke and to assure concentricity of positioning and of theactuating thrusts.

FIG. 4 illustrates a modification wherein the rack-actuating axis 70will be understood to be in a plane above the plane of the paper andtherefore on the side of the sleeve 71 opposite to that displayed forthe rack 66 and sleeve 55 in FIG. 3. The helical raceway progressionwithin sleeve 71 is therefore shown in the opposite direction to thatdisplayed in FIG. 3. In the modification of FIG. 4, a thin retainingsleeve 72 is positioned in the annular space between valve-stem guide 73and the sleeve 71. This retainer is apertured at predetermined angularand axial spacings so as to retain spaced balls in the various raceways,and thus to assure an economy of balls as well as independent action ofall balls in the various and respective race relationships. Theseresults are achieved without sacrifice of the coaxial relationshipsdiscussed above whereby no offaxis thrust component is introduced in theactuation of the valve 74.

In a specific illustrative embodiment of the FIG. 4 arrange ment, asapplied to a small-horsepower Briggs and Stratton engine having a l-inchdiameter intake valve and a Va-inch diameter exhaust valve, each havinga lift of 0.165 inch, the actuating rack travel is 0.220 inch, the anglea is about 41 42 and the angle ,3 is about 29.

FIG. 5 illustrates a modified rack structure wherein the rack member 75is cylindrical and is formed with like circumferential grooves,contoured as rack teeth over the entire rack length. As shown, the rack75 is a sleeve carried in the upper end of rod 76 forming part of thecam-follower structure. Rod 76 includes a circumferential shoulder 77defining a stop for location of a coil spring 78, preloading the racksleeve 75 against adjustable lock nuts 79 at the threaded upper end ofrod 76. Preferably, the assembly of rack 75 and rod 76 is preassembledto a suitably bossed portion 80 of the cylinder head. The lower end ofrod 76 may thus be guided by and project through boss 8%, and a pin 81retains spring-preloading means 82 within the cylinder-head structure.The cam follower itself is shown merely as a rod 83 suitably guided inthe engine block 34 to ride its particular actuating cam 85, and it willbe understood that upon assembly of the cylinder head to the block, thefollower rod structures 7683 will align, as shown, preferably withslight compressionaily loaded relief (at 86) of the shoulder 77 from thecylinder head. Rotation of cam 85 lifts the rod structure against theloading of spring means 82 and drives rack 75 through the furtherresilient loading 78. Rack 75 will be understood to engage avalve-stem-actuating sleeve 87 which is threaded in accordance withprinciples already discussed, and the spring means 78 will be availablefor slight further compression once the valve has attained its fullyseated position. Spring means 78 will thus be understood to obviate theneed for particular spring preloading within the concentricvalve-actuating structure, as at 38 in FIG. 1.

FIG. 5A illustrates a preferred offset relation, to the extentidentified A, between the axis of follower rod 83 and the centerline ofthe cam $5. This offset is such that an asymmetrical part of the endface of follower 83 is always unsupported by contact with the cam 85. Inoperation, this necessarily means a predominant torsional friction ordrag to impart slight incremental rotation of the follower rod 83 foreach cycle of the cam. Such rotation achieves a desired uniformburnishing of the cam follower end face and at the same time transmits ameasure of consistent incremental rotation to the rod 76 on which therack 75 is mounted. Thus, wear of the rack teeth is never localized atany one angular position but is rather welldistributed about the fullperiphery of tooth engagement with the sleeve 87.

FIG. 6 illustrates a modification in which the sleeve 90, which isdriven by a rack on the axis 91, is itself engaged to the valve stemguide member 92 by means of elongated splines, as at 93. Splines 93 matewith corresponding grooves as at 94 in the bore of sleeve 90. Withproper lubrication, a film of oil thus spreads torsional reaction leadsover a very extensive area, thus avoiding stress concentrations in anypart of the valve-actuating cycle and contributing to long life, with anassured concentric thrust development at all times. The structure issimplified by omission of the antifriction elements, and the angles aand [3 may approach equality, as suggested in the drawing.

FIGS. 7 to 9 illustrate several different alternative organizations fordeveloping the desired valve-actuating thrusts. In FIG. 7, theexternally threaded sleeve 95 for actuating the valve 96 is driven bymeshing teeth 97 of a sector 98 journaled for pivotal action at 99 andderiving oscillating torques from follower arm 100 integrally formedwith the sector 98. Sector teeth 97 may be straight, parallel to thepivot 99, and mesh tangentially with the external threads on sleeve 95.Cam 101 on an overhead cam shaft 102 drives arm 100 against a suitableloading spring 103.

In the arrangement of FIGS. 8 and 8A, an elongated pinion 105 mesheswith the helically threaded exterior of the sleeve 106 for actuatingvalve 107, and it will be understood that suitable means (not shown) maybe employed to translate cam actuation into driven rotary reciprocationof the pinion 105. The teeth of pinion 105 are shown straight and theymesh tangentially with the external tooth formations on sleeve 106. Theangle or already identified thus becomes the angle between the pinionaxis and a radial plane normal to the valvestem axis.

In the arrangement of FIG. 9, the helically threaded sleeve 110 isdriven by a toothed belt 111 which serves the function of the rack ofthe various forms discussed above. The belt 111 has tooth formationsmeshing with the helix of sleeve 110 throughout the full circumferentialextent of helical wrap or overlay shown in the drawing. This leavesgenerally tangentially projecting opposite ends of the belt 111. One ofthese ends may be spring-tensioned with reference to a frame part andthe other end may be drawn in accordance with a camderived profile, butin the form shown the belt 111 is continu ous, being laid over suitablepulleys or pinions 112-113, one or both of which may be driven inaccordance with the rotary reciprocating motion necessary to achieve thedesired cycle of valve actuation. In the form shown, the phantom outlineshown at 114 suggests completion of the continuous belt 111 on the backside of sleeve 110 and in clearance relation therewith.

FIG. 10 illustrates a further embodiment of the invention in which twinoverhead cam shafts 1l5--116 are provided with complementary cams 117118 for desmodromic actuation of a shuttled follower 119; cam shafts1l5116 are synchronously driven at the same speed, as suggested by themeshed 1:! gear train G,G,G,,. Follower 119 may be a rod withcircumferentially grooved rack-tooth formations 120 in mesh with thehelical threads on the outside of a valve-stem actuating sleeve 121, foroperating the valve 122 in accordance with principles already discussed.The virtue of the system of FIG. 10 is that not only is all valveactuation achieved by mechanisms carried by the cylinder head, but theactuation is positive in both stroke directions so that end play ormechanical hysteresis can be reduced to a minimum, thus assuringenhanced efficiency at high speeds of operation.

FIG. Ill is anenlarged sectional view to illustrate anotheroverhead-camshaft actuating system of the invention. The

drawing illustrates application to both the intake valve I25 and theexhaust valve I26 sewing the same cylinder 127 of an engine which may beof the familiar V variety. A single overhead camshaft 126 is suitablyjournaled in the cylinder head and it carries, in suitably spaced pairs,an intake actuating cam I29 and an exhaust actuating cam 130. A timingbelt 123 is shown connecting the camshaft 128 for 2:1 synchronized drivefrom the main camshaft; belt 123 may also serve a similar overheadcamshaft for valves in the other bank 124 of the V arrangement ofcylinders.

The follower mechanism for both cams l29130 may be generally similar,and therefore detailed discussion of the exhaust-valve-actuatingfollower 131 will suffice. Follower I31 is shown to be generallycylindrical and guided within an elongated bore in a boss or otherformation 132 in the cylinderhead casting. Follower 131 may be cupped,with a relatively thick closure wall to serve as a cam follower proper,and with a hollowed bore toreceive and locate a preloading spring 133. Athreaded plug 134 at the outer end of the guide bore for the camfollower provides frame reference for the preloading adjustment. Theguide structure R32 will be understood to be locally cut away, as at awindow opening designated 1135 for the case of theintake-valve-actuating structure. Through the window 135, the threadedperiphery of the sleeve I36 may have meshing access to thecircumferential rack-tooth formations H37 on the follower I38 whichtracks cam 1129 By virtue of the similarity of actuating mechanisms forvalves I25-1l26, similar access and meshing relationship will beunderstood to apply for the sleeve R39 and the rack-tooth formations M0.

In the arrangement of FIG. ii, the preloading spring ME for theexhaust-valve actuating structure will be seen to supply the desiredresilient loading of the valve-seated position, and auxiliary sleeve 142within the main sleeve I39 affords adjustment of this seatedrelationship. Similar adjustment and preloading are of course availablefor the intake-valve actuating mechanism, and it will be noted thataccess for either or both of these adjustments is very simply achievedby removing the hollow bolt structure 1453 which surrounds the sparkplug M4 and which retains a shroud or closure pan I45, against sealinggaskets, over the entire assembly.

FIG. R2 is a schematic illustration of another desmodromic cam-actuatingsystem, representing an alternative drive for the sleeve 150 ofactuating mechanism for a valve ESE. In FIG. l2, a single follower rodE52 is provided at its outer end with a rack portion 153 and at itsinner end with two like cam-follower rolls l53l5d mounted atdiametrically opposite sides of the camshaft H55 and on opposite facesof the'follower rod I52. In the vicinity of cam-following engagement,rod I52 is cut out at 156 to define spaced elongated parallel pilotingwalls for guided location on the periphery of the camshaft 155; eachfollower rod 152 is located axially between an upstroke cam i157 and adownstroke cam I58 which are respectively in constant contact with thefollower rolls I53154L Preferably, the camshaft is characterized by anelongated cylindrical bore 159 having radially ported connection, as at160, in the regions between pairs of cams l57--ll58. Such passagesprovide a means of freely circulating lubricant to assure smoothdesmodromic cam action. To assure ready assembly of the follower rod 152to its camshaft, a parting line 16h suggests that rod 1152 is formed oftwo like abutting elongated halves, secured together by screws atsuitably spaced locations 362-162' in the vicinity of cam-followercontact.

FIGS. M and 115 are very schematic illustrations of pressure-fluidoperated systems for concentric valve-actuating mechanism operating anexternally threaded sleeve 165 for valve 166. In FIG. M, a double-actinghydraulic or pneumatic cylinder 167 with head and tail port connections168-169 imparts reciprocating displacement to a rack arm on actuatingaxis 170. The rack arm may be merely an end formation of a piston rod171 and may be understood to be in mesh with the helix formations onsleeve 165. Cyclically reversing fluid pressures are delivered to theports 168-169 by suitable means merely suggested by heavy dashed lines172-ll73; such means will be understood to include actuating followerswhich track the respective upstroke and downstroke cams l74-175constituting the pair required for operation of valve 166. Cams 174-175are mounted on a camshaft 176 common to all valve-actuating cams.

In FIG. 15, the double-acting pressure-operated rack actuator of FIG. 14will be recognized but its operation is governed by an electricalcontrol system involving limit switches 177- I78 which track therespective profiles of cams 174-475 to determine alternating excitationof reversing solenoids l79 use. Solenoids 179-180 are supplied by source181 to determine distribution (at valve 182) of pressurized fluid inline 169 or in line I68, as the case may be, for valve-closure and forvalve-opening strokes at 166. The solenoid-operated distribution valve382 may be of well-known commercially available construction and istherefore not shown in detail. The fluid system is shown to rely upon asupply pump E83 and a pressure-fluid return system including a sump 184.Because the fluid system of FIG. 15 has the inherent capacity to achievevery rapid valve-actuating displacements, I indicate the desirability ofproviding dashpot action, suggested at 185, to cushion the actuatingmotions. A manual adjustment at 186 provides selection of the bleed todetermine dashpot action.

The description of FIGS. M and 15 as having fluid components will beunderstood to involve a generic use of the expression. In other words,the principles of FIG. 14 and 15 are applicable whatever the relativecompressibility of the fluid involved. Thus, these systems may employpressurized relatively incompressible liquids such as oils, or they mayemploy pressurized more compressible fluids such as air. Pneumatic valveoperation is thus expressly contemplated by the disclosure.

It is considered important to the invention that the essence ofrack-and-pinion contact, in the various forms disclosed, involvesprimarily point contact at any single instant of time, regardless ofposition in the reciprocating cycle. Point contact necessarily followsfrom a tangential rack-tooth engagement at the helical pinion teeth,assuming involute or nonslip profile design for the meshing teeth.

From a wear standpoint, it is a matter of relative insignificance thatrack reciprocation is accompanied by axial displacement of the helicallythreaded sleeve (pinion), since point-contact is always at the essenceof the engagement. Point contact applies for the straight-rack (as inFIG. 2) forms and for the rack-of-revolution forms (as in FIG. 5).

it will be seen that l have described improved valve-actuating mechanisminherently capable of avoiding problems of conventional mechanisms andmaking for engine constructions having substantially extended lifeexpectancy and materially improved operating efficiency, particularly athigh operating speeds. Specifically, my invention points the way toelimination of the valve train as a major problem of engine life andoperation. Valve actuation becomes virtually frictionless, and there canbe no off-axis development of valve-actuating thrusts. Servicing accessand initial installation are facilitated by using the key technique (32)to position and retain a valveactuating preassembly; valve-seatingpreload being a matter of simple adjustment, readily accessible at thecylinder head, as

in FIG. 11 for the ends of the valve stems (at M2), or as in FIG. 5 forthe end of the cam-follower rods (at 79).

My construction enables simplification of parts and the use oflighter-weight components, as compared to present systems. Lower forcesare needed for valve actuation, so that friction (where it exists)necessarily involves less wear. The unitized nature of each valveactuator permits greater flexibility to the designer as to valvepositioning, and the variety of alternate means to effectactuating-sleeve oscillation further enhances the flexibility ofapplication to specific problems. Obvious advantages of increasedthermal efficiency, including avoidance of hotspots, flow from thepurely axial nature of all valve-actuating thrusts. From the designersviewpoint, my invention offers the considerable advantage of eliminatingall angularity effects which must be accounted for in rocker-armdesigns; the designer can thus rely on the completely linear relationbetween force transmission and displacement, from cam to valve. Valvereaction to the cam profile can be more instantaneous, there being noneed for hysteresis-producing gaps or clearances in the valve train. Thelight weight and lower inertia of components and lesser spring forces ofmy invention mean substantial reduction of spring surge and otherelasticity effects in the valve train; these factors are virtuallycompletely eliminated in desmodromic versions.

Although the invention has been described in detail for the forms shown,it will be understood that modifications may be made within the scope ofthe invention as defined by the claims.

What 1 claim is:

1. Valve mechanism, comprising a valve body having a seat and a valvemember and stem guided by said body for axial reciprocation between openand closed relation with said seat, a first sleeve member carried bysaid body and having a guide bore for said stem, a second sleeve memberhaving a part in helically cammed axial overlap with said first sleevemember and with a part connected to said stem, and actuating meansincluding reciprocating rack-and-pinion means for rotary reciprocationof said second sleeve member, whereby rack reciprocation imparts axialreciprocation to said valve member with respect to said seat.

2. Valve mechanism according to claim 1, in which the pinion of saidrack-and-pinion means is carried by said second sleeve member.

3. Valve mechanism according to claim 1, in which the pinion of saidrack-and-pinion means is an external formation of said second sleevemember.

4. Valve mechanism according to claim 1, in which said rack-and-pinionmeans is so positioned that raclr-and-pinion action takes place withinthe axial extent of helically cammed engagement between said sleeves.

5. Valve mechanism according to claim 1, in which said rack-and-pinionmeans is so positioned that the rack-andpinion reaction vector is offsetfrom the valve-reciprocation axis and is oriented in substantially thedirection of the nearest tangent to the locus of helically cammedengagement between said sleeves.

6. Valve mechanism according to claim 3, in which said valve and stemare free to rotate in the connection thereof to said second sleevemember.

7. Valve mechanism according to claim 1, in which the connection betweensaid stem and said second sleeve member includes longitudinallyadjustable means, whereby, for a given rack stroke, adjustment may bemade for the degree of valve seat engagement at the valve-closedposition. I

8. Valve mechanism according to claim 1, in which said helically cammedoverlap includes a threaded engagement between said sleeve members.

9. Valve mechanism according to claim 1, in which said helically cammedoverlap includes plural antifriction elements riding matched inner andouter helical race grooves in the region of axial overlap of said sleevemembers.

10. Valve mechanism according to claim 1, in which said actuating meansincludes a driven rotary cam, and cam-follower means including the rackof said rack-and-pinion means.

11. Valve mechanism according to claim 10, in which said follower meansincludes a follower element with an adjustably securable connection tosaid rack, whereby adjustment at said connection provides adjustment ofthe degree of valve-seat engagement at the valve-closed position.

12. Valve mechanism according to claim 10, in which said body includesguide means for the nonrotatable guided longitudinal reciprocation ofsaid rack.

13. Valve mechanism according to claim 10, in which said body includesguide means for the rotatable guided longitudinal reciprocation of saidrack, the teeth of said rack being a formation of revolution about theaxis of rack reciprocation.

14. Valve mechanism according to claim 13, in which said body includesmeans for the rotatable guided reciprocation of the element of saidcam-follower means which rides said cam,

and in which the net contact region between said cam and saidfollower-element is offset from the guide axis for said element.

15. Valve mechanism according to claim 10, in which said cam is of thedesmodromic variety.

16. Valve support and actuating mechanism for the poppet valve of aninternal-combustion engine, comprising an elongated guide bushingadapted to be secured to an engine, said bushing having a bore for therotatable longitudinally reciprocated guidance of the stem of a poppetvalve, a sleeve axially overlapping part of said bushing, theoverlapping portions of said sleeve and bushing having helically cammedengagement, said sleeve including connection means for the removableconnection of the tail of a poppet-valve stem thereto, said sleevehaving external pinion-tooth formations for actuated engagement bymating driver teeth external to the valve axis.

17. Mechanism according to claim 16, in which the said pinion-toothformations are helically pitched in the direction opposite to the pitchof said helically cammed engagement.

1%. Mechanism according to claim 16, in which the helical lead of saidpinion-tooth formations is substantially equal in magnitude but oppositein direction to that of said helically cammed engagement.

19. Mechanism according to claim 16, in which said bushing includes atone end a first elongated generally cylindrical adapter-mount portionfor reception in a mounting bore of an engine frame, a radial shoulderintermediate the helically cammed and adapter-mount portions of saidbushing for limiting the insertion-mounting of said bushing in theengine frame, and locating and locking means off the axis of saidbushing and serving to retain the axial and angular position of thebushing when inserted in the engine frame.

20. Mechanism according to claim 16, in which the helical lead of saidpinion-tooth formations exceeds the magnitude and is opposite indirection to that of said helically cammed engagement.

21. Mechanism according to claim 20, in which the helical lead of saidpinion-tooth formations is in the range of substantially 35 to 45.

22. Mechanism according to claim 20, in which the helical lead of saidpinion-tooth formations is substantially 41 to 42.

23. Mechanism according to claim 20, in which the helical lead of saidcammed engagement is in the range of substantially 25 to 35.

24. Mechanism according to claim 20, in which the helical lead of saidcammed engagement is substantially 29.

25. in combination, an internal-combustion engine including a cam shaftand having a cylinder and inlet and exhaust ports communicating withsaid cylinder, inlet and exhaust poppet valves having guided support insaid engine for opening and closing said ports, and valve-actuatingmechanism driven by said cam shaft for actuating said valves and for therandom angular indexing of said valves with each actuating cyclethereof; said mechanism comprising, for each valve, reciprocatingcam-follower means tracking a part of said cam shaft and a connectionfrom said cam-follower means to its valve, said connection including twooverlapping sleeves in helically cammed engagement, one of said sleevesbeing referenced to the engine frame and the other of said sleevesincluding means independent of said helically cammed engagement andresponding to cam-follower reciprocation to rotationally reciprocatesaid other sleeve, the valve stem being freely rotatably connected tosaid other sleeve.

26. In combination, an internal-combustion engine including a cam shaftand having a cylinder and inlet and exhaust ports communicating withsaid cylinder, inlet and exhaust poppet valves having guided support insaid engine for opening and closing said ports, and valve-actuatingmechanism driven by said cam shaft for actuating said valves and for therandom angular indexing of said valves with each actuating cyclethereof; said mechanism comprising, for each valve, reciprocatingcarnefollower means tracking a part of said cam shaft and a connectionfrom said camfollower means to its valve, said connection includingmeans referenced to the engine frame and responding to cam-followerreciprocation to impart to its valve a reciprocating cycle that is bothangular and axial; said connection including a helical-track ballbearing on the axis of valve actuation, said bearing comprising innerand outer elements having matched helical ball races in theiroverlapping adjacent surfaces, balls in said races, one of said elementsbeing fixed to the engine frame, the other of said elements having arotary-reciprocating driven connection to said cam-follower means, thevalve-stem connection being made to said other element, with the valvefreely rotatable.

27. The combination of claim 26, in which said ball bearing includesretainer means retaining adjacent balls in spaced relation in the ballcomplement of each race.

23. The combination of claim 27, in which a single retainer serves ballsof all races.

29. in combination, an internal-combustion engine including a cam shaftand having a cylinder and inlet and exhaust ports communicating withsaid cylinder, inlet and exhaust poppet valves having guided support insaid engine for opening and closing said ports, and valve-actuatingmechanism driven by said cam shaft for actuating said valves and for therandom angular indexing of said valves with each actuating cyclethereof; said mechanism comprising, for each valve, reciprocatingcam-follower means tracking a part of said cam shaft and a connectionfrom said cam-follower means to its valve, said connection includingmeans referenced to the engine frame and responding to cam-followerreciprocation to impart to its valve a reciprocating cycle that is bothangular and axial; said connection including matched inner and outerhelically splined elements with the helix axis on the axis of valveactuation, one of said elements being fixed to the engine frame, theother of said elements having a rotary-reciprocating driven connectionto said cam-follower means, the valvestem connection being made to saidother element, with the valve freely rotatable.

30. in combination, an internal-combustion engine including a cam shaftand having a cylinder and inlet and exhaust ports communicating withsaid cylinder, inlet and exhaust poppet valves having guided support insaid engine for opening and closing said ports, and valve-actuatingmechanism driven by said cam shaft, said valve-actuating mechanismincluding cam-follower means for each valve and tracking a part of saidcam shaft, preloaded spring means independent of the valve closingforces and acting between the engine frame and said cam-follower meansfor assuring earn-tracking, and means including a helically cammedsleeve referenced to the engine frame and connected to its valve, saidsleeve having a rotary reciprocating driven connection to saidcam-follower means.

31. The combination of claim 30 in which the direction of preload ofsaid spring means biases said cam-follower means in the valve-openingdirection.

32. in combination, an internal-combustion engine comprising spacedparallel cam shafts in synchronized relation, complementary desmodromiccams on said cam shafts, a reciprocating follower tracking a pair ofcomplementary cams on said cam shafts, a valve having an elongated stem,valvestem guide means, a rotatable sleeve connected to said valve stemand in helically cammed engagement with said valvestem guide means on anaxis concentric with the axis of valvestem guidance, and meansconnecting said sleeve to said follower to impart to said sleevecyclical oscillations about the sleeve axis in accordance withreciprocations of said follower.

33. in combination, an internal-combustion engine comprising a cam shafthaving a pair of desmodromic cams, a reciprocating follower trackingboth said cams, a valve having an elongated stem, valve-stem guidemeans, a rotatable sleeve connected to said valve stem and in helicallycammed engagement with said valve-stem guide means on an axis concentricwith the axis of valve-stem guidance, and means connecting said sleeveto said follower to impart to said sleeve cyclical oscillations aboutthe sleeve axis in accordance with reciprocations of said follower.

3%. As an article of manufacture, a unitary valve-stem guide andlongitudinal actuator, comprising an elongated guide member having atone end means for secure removable attachment to an engine frame andincluding at the other end a generally cylindrical projection, elongatedvalve-stem guide means extending through said member in concentricrelation with said projection, and a sleeve carried concentrically aboutsaid projection and having a helically cammed rotary and longitudinaldisplacement relation to said projection.

35. The article of claim 34, in which said sleeve has external helicalthreads of helix-advance direction opposed to that of said cammedrelation.

36. The article of claim 34, in which the end of said sleeve projectsaxially beyond said projection and includes means for the selectiveattachment of a valve stem.

37. The article of claim 36, in which said sleeve comprises a firstsleeve part in helically cammed relation to said projection and a secondsleeve part in threaded longitudinally adjustable relation to said firstsleeve part and at the axially projecting end thereof, said selectiveattachment means being on said second sleeve part.

38. The article of claim 34, in which plural splines establish the saidhelically cammed engagement.

39. The article of claim 34, in which plural balls in pluralcorresponding helical races in said projection and within said sleeveestablish the said helically cammed engagement.

40. in combination, an internal-combustion engine including a cylinderhead and comprising a cam shaft with a pair of cams and joumaled forrotation in said head, intake and exhaust port and valve structure insaid head on opposite sides of said cam shaft, an intake-valve actuatorincluding a rotary sleeve connected to its valve on a valve-actuatingaxis, an exhaust-valve actuator including a rotary sleeve connected toits valve on a valve-actuating axis, said axes being inclined towardeach other on opposite sides of said cam shaft, each sleeve beingexternally helically threaded, and rack followers meshing with saidrespective sleeve threads and tracking said cams in opposite directionsbut substantially in a plane common to the axis of cam shaft rotation.

41. Valve mechanism, comprising a valve body having a seat and a valvemember and stem guided by said body for axial reciprocation between openand closed relation with said seat, a first sleeve member carried bysaid body and having a guide bore for said stem, a second sleeve memberhaving a part in helically cammed axial overlap with said first sleevemember and having a part connected to said stem, and actuating meansincluding reciprocating driving means connected for rotary reciprocationof said second sleeve, whereby rotary reciprocation imparted to saidsecond sleeve member imparts axial reciprocation to said valve memberwith respect to said seat.

42. Valve mechanism according to claim 41, in which said actuating meansincludes a cam-and-follower mechanism determining the reciprocationimparted to said second sleeve member.

43. Valve mechanism according to claim 42, in which said actuating meansincludes fluid-pressure operated means between said cam-and-followermechanism and said second sleeve member.

44. Valve mechanism according to claim 41, in which said actuating meansincludes fluid-pressure operated means determining the reciprocationimparted to said second sleeve member, and recycling program meansincluding pressurefluid reversing valve means in controlling relationwith said fluid-pressure operated means.

45. Valve mechanism according to claim 42, in which said actuating meansincludes a belt in positive direct-driving relation with said secondsleeve member.

46. Valve mechanism according to claim 42, in which said second sleevemember has a toothed periphery, and in which said actuating meansincludes means having a reciprocating geared engagement to said toothedperiphery.

47. Valve mechanism according to claim 46, in which said last-definedmeans includes a pinion gear.

48. Valve mechanism according to claim 46, in which said last-definedmeans includes a sector gear and in which an arm effectively integralwith said gear is part of said cam-and-follower means.

49. Valve mechanism comprising a body element having an elongated guidebore, a valve element including a stem supported in said bore andslidably guided thereby for longitudinal and rotary motion, andvalve-actuating mechanism referenced to said element and including alinear-reciprocating to rotary-reciprocating coupling wherein arotaryreciprocating output element is guided for rotary-reciprocation onand axial reciprocation along the axis of said guide bore, saidmechanism including a linear-reciprocating input element reciprocable onan axis angularly offset from the guide-bore axis, said angular offsetbeing in the range intermediate a direction parallel to and a directionnormal to the guide-bore whereby thrusts imparted to said output elementand occasioned by reciprocation of said input element are necessarilycharacterized by a combination of axial and rotary-reciprocating thrustcomponents, and an axially retaining interconnection between said outputelement and said valve stem.

50. The mechanism according to claim 49, in which said interconnectionis characterized by freedom for relative rotation of said valve elementand of said output element.

51. The mechanism according to claim 49, in which said valve-actuatingmechanism includes between said input and output elements aninterconnection member freely rotatable on the linear-reciprocation axisof said input member.

1. Valve mechanism, comprising a valve body having a seat and a valvemember and stem guided by said body for axial reciprocation between openand closed relation with said seat, a first sleeve member carried bysaid body and having a guide bore for said stem, a second sleeve memberhaving a part in helically cammed axial overlap with said first sleevemember and with a part connected to said stem, and actuating meansincluding reciprocating rack-and-pinion means for rotary reciprocationof said second sleeve member, whereby rack reciprocation imparts axialreciprocation to said valve member with respect to said seat.
 2. Valvemechanism according to claim 1, in which the pinion of saidrack-and-pinion means is carried by said second sleeve member.
 3. Valvemechanism according to claim 1, in which the pinion of saidrack-and-pinion means is an external formation of said second sleevemember.
 4. Valve mechanism according to claim 1, in which saidrack-and-pinion means is so positioned that rack-and-pinion action takesplace within the axial extent of helically cammed engagement betweensaid sleeves.
 5. Valve mechanism according to claim 1, in which saidrack-and-pinion means is so positioned that the rack-and-pinion reactionvector is offset from the valve-reciprocation axis and is oriented insubstantially the direction of the nearest tangent to the locus ofhelically cammed engagement between said sleeves.
 6. Valve mechanismaccording to claim 1, in which said valve and stem are free to rotate inthe connection thereof to said second sleeve member.
 7. Valve mechanismaccording to claim 1, in which the connection between said stem and saidsecond sleeve member includes longitudinally adjustable means, whereby,for a given rack stroke, adjustment may be made for the degree ofvalve-seat engagement at the valve-closed position.
 8. Valve mechanismaccording to claim 1, in which said helically cammed overlap includes athreaded engagement between said sleeve members.
 9. Valve mechanismaccording to claim 1, in which said helically cammed overlap includesplural antifriction elements riding matched inner and outer helical racegrooves in the region of axial overlap of said sleeve members.
 10. Valvemechanism according to claim 1, in which said actuating means includes adriven rotary cam, and cam-follower means including the rack of saidrack-and-pinion means.
 11. Valve mechanism according to claim 10, inwhich said follower means includes a follower element with an adjustablysecurable connection to said rack, whereby adjustment at said connectionprovides adjustment of the degree of valve-seat engagement at thevalve-closed position.
 12. Valve mechanism according to claim 10, inwhich said body includes guide means for the nonrotatable guidedlongitudinal reciprocation of said rack.
 13. Valve mechanism accordingto claim 10, in which said body includes guide means for the rotatableguided longitudinal reciprocation of said rack, the teeth of said rackbeing a formation of revolution about the axis of rack reciprocation.14. Valve mechanism according to claim 13, in which said body includesmeans for the rotatable guided reciprocation of the element of saidcam-follower means which rides said cam, and in which the net contactregion between said cam and said follower-element is offset from theguide axis for said element.
 15. Valve mechanism according to claim 10,in which said cam is of the desmodromic variety.
 16. Valve support andactuating mechanism for the poppet valve of an internal-combustionengine, comprising an elongated guide bushing adapted to be secured toan engine, said bushing having a bore for the rotatable longitudinallyreciprocated guidance of the stem of a poppet valve, a sleeve axiallyoverlapping part of said bushing, the overlapping portions of saidsleeve and bushing having helically cammed engagement, said sleeveIncluding connection means for the removable connection of the tail of apoppet-valve stem thereto, said sleeve having external pinion-toothformations for actuated engagement by mating driver teeth external tothe valve axis.
 17. Mechanism according to claim 16, in which the saidpinion-tooth formations are helically pitched in the direction oppositeto the pitch of said helically cammed engagement.
 18. Mechanismaccording to claim 16, in which the helical lead of said pinion-toothformations is substantially equal in magnitude but opposite in directionto that of said helically cammed engagement.
 19. Mechanism according toclaim 16, in which said bushing includes at one end a first elongatedgenerally cylindrical adapter-mount portion for reception in a mountingbore of an engine frame, a radial shoulder intermediate the helicallycammed and adapter-mount portions of said bushing for limiting theinsertion-mounting of said bushing in the engine frame, and locating andlocking means off the axis of said bushing and serving to retain theaxial and angular position of the bushing when inserted in the engineframe.
 20. Mechanism according to claim 16, in which the helical lead ofsaid pinion-tooth formations exceeds the magnitude and is opposite indirection to that of said helically cammed engagement.
 21. Mechanismaccording to claim 20, in which the helical lead of said pinion-toothformations is in the range of substantially 35* to 45*.
 22. Mechanismaccording to claim 20, in which the helical lead of said pinion-toothformations is substantially 41* to 42*.
 23. Mechanism according to claim20, in which the helical lead of said cammed engagement is in the rangeof substantially 25* to 35*.
 24. Mechanism according to claim 20, inwhich the helical lead of said cammed engagement is substantially 29*.25. In combination, an internal-combustion engine including a cam shaftand having a cylinder and inlet and exhaust ports communicating withsaid cylinder, inlet and exhaust poppet valves having guided support insaid engine for opening and closing said ports, and valve-actuatingmechanism driven by said cam shaft for actuating said valves and for therandom angular indexing of said valves with each actuating cyclethereof; said mechanism comprising, for each valve, reciprocatingcam-follower means tracking a part of said cam shaft and a connectionfrom said cam-follower means to its valve, said connection including twooverlapping sleeves in helically cammed engagement, one of said sleevesbeing referenced to the engine frame and the other of said sleevesincluding means independent of said helically cammed engagement andresponding to cam-follower reciprocation to rotationally reciprocatesaid other sleeve, the valve stem being freely rotatably connected tosaid other sleeve.
 26. In combination, an internal-combustion engineincluding a cam shaft and having a cylinder and inlet and exhaust portscommunicating with said cylinder, inlet and exhaust poppet valves havingguided support in said engine for opening and closing said ports, andvalve-actuating mechanism driven by said cam shaft for actuating saidvalves and for the random angular indexing of said valves with eachactuating cycle thereof; said mechanism comprising, for each valve,reciprocating cam-follower means tracking a part of said cam shaft and aconnection from said cam-follower means to its valve, said connectionincluding means referenced to the engine frame and responding tocam-follower reciprocation to impart to its valve a reciprocating cyclethat is both angular and axial; said connection including ahelical-track ball bearing on the axis of valve actuation, said bearingcomprising inner and outer elements having matched helical ball races intheir overlapping adjacent surfaces, balls in said races, one of saidelements being fixed to the engine frame, the other of said elementshaving a rotary-reciproCating driven connection to said cam-followermeans, the valve-stem connection being made to said other element, withthe valve freely rotatable.
 27. The combination of claim 26, in whichsaid ball bearing includes retainer means retaining adjacent balls inspaced relation in the ball complement of each race.
 28. The combinationof claim 27, in which a single retainer serves balls of all races. 29.In combination, an internal-combustion engine including a cam shaft andhaving a cylinder and inlet and exhaust ports communicating with saidcylinder, inlet and exhaust poppet valves having guided support in saidengine for opening and closing said ports, and valve-actuating mechanismdriven by said cam shaft for actuating said valves and for the randomangular indexing of said valves with each actuating cycle thereof; saidmechanism comprising, for each valve, reciprocating cam-follower meanstracking a part of said cam shaft and a connection from saidcam-follower means to its valve, said connection including meansreferenced to the engine frame and responding to cam-followerreciprocation to impart to its valve a reciprocating cycle that is bothangular and axial; said connection including matched inner and outerhelically splined elements with the helix axis on the axis of valveactuation, one of said elements being fixed to the engine frame, theother of said elements having a rotary-reciprocating driven connectionto said cam-follower means, the valve-stem connection being made to saidother element, with the valve freely rotatable.
 30. In combination, aninternal-combustion engine including a cam shaft and having a cylinderand inlet and exhaust ports communicating with said cylinder, inlet andexhaust poppet valves having guided support in said engine for openingand closing said ports, and valve-actuating mechanism driven by said camshaft, said valve-actuating mechanism including cam-follower means foreach valve and tracking a part of said cam shaft, preloaded spring meansindependent of the valve closing forces and acting between the engineframe and said cam-follower means for assuring cam-tracking, and meansincluding a helically cammed sleeve referenced to the engine frame andconnected to its valve, said sleeve having a rotary reciprocating drivenconnection to said cam-follower means.
 31. The combination of claim 30in which the direction of preload of said spring means biases saidcam-follower means in the valve-opening direction.
 32. In combination,an internal-combustion engine comprising spaced parallel cam shafts insynchronized relation, complementary desmodromic cams on said camshafts, a reciprocating follower tracking a pair of complementary camson said cam shafts, a valve having an elongated stem, valve-stem guidemeans, a rotatable sleeve connected to said valve stem and in helicallycammed engagement with said valve-stem guide means on an axis concentricwith the axis of valve-stem guidance, and means connecting said sleeveto said follower to impart to said sleeve cyclical oscillations aboutthe sleeve axis in accordance with reciprocations of said follower. 33.In combination, an internal-combustion engine comprising a cam shafthaving a pair of desmodromic cams, a reciprocating follower trackingboth said cams, a valve having an elongated stem, valve-stem guidemeans, a rotatable sleeve connected to said valve stem and in helicallycammed engagement with said valve-stem guide means on an axis concentricwith the axis of valve-stem guidance, and means connecting said sleeveto said follower to impart to said sleeve cyclical oscillations aboutthe sleeve axis in accordance with reciprocations of said follower. 34.As an article of manufacture, a unitary valve-stem guide andlongitudinal actuator, comprising an elongated guide member having atone end means for secure removable attachment to an engine frame andincluding at the other end a generally cylindrical projection, elongatedvalve-stem guide means extending through said member in concentricrelation with said projection, and a sleeve carried concentrically aboutsaid projection and having a helically cammed rotary and longitudinaldisplacement relation to said projection.
 35. The article of claim 34,in which said sleeve has external helical threads of helix-advancedirection opposed to that of said cammed relation.
 36. The article ofclaim 34, in which the end of said sleeve projects axially beyond saidprojection and includes means for the selective attachment of a valvestem.
 37. The article of claim 36, in which said sleeve comprises afirst sleeve part in helically cammed relation to said projection and asecond sleeve part in threaded longitudinally adjustable relation tosaid first sleeve part and at the axially projecting end thereof, saidselective attachment means being on said second sleeve part.
 38. Thearticle of claim 34, in which plural splines establish the saidhelically cammed engagement.
 39. The article of claim 34, in whichplural balls in plural corresponding helical races in said projectionand within said sleeve establish the said helically cammed engagement.40. In combination, an internal-combustion engine including a cylinderhead and comprising a cam shaft with a pair of cams and journaled forrotation in said head, intake and exhaust port and valve structure insaid head on opposite sides of said cam shaft, an intake-valve actuatorincluding a rotary sleeve connected to its valve on a valve-actuatingaxis, an exhaust-valve actuator including a rotary sleeve connected toits valve on a valve-actuating axis, said axes being inclined towardeach other on opposite sides of said cam shaft, each sleeve beingexternally helically threaded, and rack followers meshing with saidrespective sleeve threads and tracking said cams in opposite directionsbut substantially in a plane common to the axis of cam shaft rotation.41. Valve mechanism, comprising a valve body having a seat and a valvemember and stem guided by said body for axial reciprocation between openand closed relation with said seat, a first sleeve member carried bysaid body and having a guide bore for said stem, a second sleeve memberhaving a part in helically cammed axial overlap with said first sleevemember and having a part connected to said stem, and actuating meansincluding reciprocating driving means connected for rotary reciprocationof said second sleeve, whereby rotary reciprocation imparted to saidsecond sleeve member imparts axial reciprocation to said valve memberwith respect to said seat.
 42. Valve mechanism according to claim 41, inwhich said actuating means includes a cam-and-follower mechanismdetermining the reciprocation imparted to said second sleeve member. 43.Valve mechanism according to claim 42, in which said actuating meansincludes fluid-pressure operated means between said cam-and-followermechanism and said second sleeve member.
 44. Valve mechanism accordingto claim 41, in which said actuating means includes fluid-pressureoperated means determining the reciprocation imparted to said secondsleeve member, and recycling program means including pressure-fluidreversing valve means in controlling relation with said fluid-pressureoperated means.
 45. Valve mechanism according to claim 42, in which saidactuating means includes a belt in positive direct-driving relation withsaid second sleeve member.
 46. Valve mechanism according to claim 42, inwhich said second sleeve member has a toothed periphery, and in whichsaid actuating means includes means having a reciprocating gearedengagement to said toothed periphery.
 47. Valve mechanism according toclaim 46, in which said last-defined means includes a pinion gear. 48.Valve mechanism according to claim 46, in which said last-defined meansincludes a sector gear and in which an arm effectively integral withsaid gear is part of said cam-and-follower means.
 49. Valve mechanismcomprisinG a body element having an elongated guide bore, a valveelement including a stem supported in said bore and slidably guidedthereby for longitudinal and rotary motion, and valve-actuatingmechanism referenced to said element and including alinear-reciprocating to rotary-reciprocating coupling wherein arotary-reciprocating output element is guided for rotary-reciprocationon and axial reciprocation along the axis of said guide bore, saidmechanism including a linear-reciprocating input element reciprocable onan axis angularly offset from the guide-bore axis, said angular offsetbeing in the range intermediate a direction parallel to and a directionnormal to the guide-bore whereby thrusts imparted to said output elementand occasioned by reciprocation of said input element are necessarilycharacterized by a combination of axial and rotary-reciprocating thrustcomponents, and an axially retaining interconnection between said outputelement and said valve stem.
 50. The mechanism according to claim 49, inwhich said interconnection is characterized by freedom for relativerotation of said valve element and of said output element.
 51. Themechanism according to claim 49, in which said valve-actuating mechanismincludes between said input and output elements an interconnectionmember freely rotatable on the linear-reciprocation axis of said inputmember.